1. Field of Invention
The field of this invention relates to methods and apparatus for continuous electrophoresis, that is, the separating of mixtures of microscopic charged particles in samples. More specifically, this method of continuously separating mixtures of microscopic charged particles relates to apparatus having distributive output ports for the collection of such particles in an electrical field.
2. Related Art
There are numerous methods of continuously separating mixtures of particles in electrophoresis devices. These are typified by U.S. Pat. No. 3,412,008 to STRICKLER, U.S. Pat. No. 4,061,560 to HANNIG, and U.S. Pat. No. 4,310,418 to ROSE/RICHMAN. The free flow electrophoretic process described in such patents is the result of a combination of several phenomena. The process generally utilizes a continuous laminar flow of a carrier fluid or buffer 5 through a chamber with multiple outlets as shown in FIGS. 1, 2, and 3. The sample stream 1 containing a protein or other cell particles is input into this flow and an electrical field applied to the flow in the direction generally perpendicular to the flow. The basis for separation is the resulting electrophoresis of the samples or the motion of charged particles in an electrical field. This motion is the result of the force, on the particles, which is proportional to the charge and the electrical field strength. Under the influence of this force, the particles are accelerated in a direction lateral to flow direction and approach a terminal velocity, which is the velocity reached when the force of the viscous drag on the particles and the force of the electrical field reach equilibrium. The basis for separation is that different particles generally have different lateral terminal velocities and, therefore, leave the chamber through a different exit port strategically placed for collection, thereby providing a separation device. A typical wide chamber as shown in FIG. 1 provides sufficient width to accommodate the range of mobility predicted for the sample 1. The phenomena is quantified by a characteristic known as particle mobility which is the velocity component in the direction of the electric field divided by the electrical field strength. In other prior related art, the electric field is applied across a thickness dimension of an electrophoresis chamber as shown in FIGS. 2 and 3 and a sample 1 to be separated is inserted in the laminar flow layer in the chamber. Such a method was proposed to NASA in the mid-1970s by A. STRICKLER of Beckman Instruments. This method was found to have two major faults. First, the heating of the buffer due to the electrical field and heat removal from the walls of the chamber caused convection cells which disrupted the flow at the output end of the chamber. Second, attempts to suppress the convection flow by limiting the chamber thickness resulted in very thin sample and outlet fraction layers which mixed by concentration driven diffusion thereby spoiling the separation. Electrophoresis chambers of this type have been addressed by PHILPOT in U.S. Pat. No. 3,616,453 where flow is layered between a fixed inner cylindrical wall and a rotating outer cylindrical wall causing stabilizing monotonic increases in angular momentum from the inner cylinder to the outer cylinder. The rotating cylindrical approach, while addressing these problems, results in a significant increase in mechanical complexity and potential reliability problems. The PHILPOT device as configured has 30 output fractions limiting its resolution potential. However, a relatively large sample cross-section gives it a large throughput potential.